Rainwater left untreated in cooling towers atop city-owned Harlem Hospital fueled the Big Apple’s deadliest Legionnaire’s disease outbreak in a decade, the Rev. Al Sharpton charged Tuesday.

Legionnaires’ disease is a rare condition, and incidence is hard to estimate because diagnosis requires a suspicion of disease and ordering of the tests needed for confirmation, said Krishna Thavarajah, MD, a pulmonologist and director of the Interstitial Lung Disease Program at Henry Ford Hospital, Detroit, in an interview.

A deadly Legionnaires' disease outbreak in New York City has set health and community leaders on a campaign to educate the public on ways to prevent the bacteria from growing and spreading.